Irma headed towards Puerto Rico, Haiti, Cuba and Florida, with potential for coastal storm surges of up to six metres.

A powerful Atlantic Ocean hurricane has made its first landfall in the islands of the northeast Caribbean, en route to Puerto Rico, the Dominican Republic, Haiti and Cuba before possibly heading for the US state of Florida.

Hurricane Irma carries the potential for coastal storm surges of up to six metres above normal tide levels, the Miami-based National Hurricane Centre said on Wednesday.

The National Weather Service said Puerto Rico had not seen a hurricane of Irma's magnitude since Hurricane San Felipe in 1928, which killed a total of 2,748 people in Guadeloupe, Puerto Rico and Florida.

Warm water is fuel for hurricanes and Irma is over water that is 1C warmer than normal.

The 26C water that hurricanes need goes about 80 metres deep, said Jeff Masters, meteorology director of the private forecasting service Weather Underground.

The eye of Irma passed over Barbuda at about 1:47am local time (05:47 GMT), the National Weather Service said.

Residents said over local radio that phone lines went down. Heavy rain and winds buffeted the neighbouring island of Antigua, sending debris flying as people huddled in their homes or government shelters.

Officials warned people to seek protection from Irma's "onslaught" in a statement that closed with: "May God protect us all."

"This is not an opportunity to go outside and try to have fun with a hurricane," US Virgin Islands Governor Kenneth Mapp said. "It's not time to get on a surfboard."

The Category 5 storm had maximum sustained winds of 295km per hour (kph), said the National Hurricane Centre.

Its forecast late on Tuesday was for the winds to fluctuate slightly but for the storm to remain at Category 4 or 5 strength for the next day or two.

Dangerous winds

The most dangerous winds, usually nearest to the eye, were forecast to pass near the northern Virgin Islands and near or just north of Puerto Rico through Wednesday.

On Antigua Island, people who live in low-lying areas were staying with friends and relatives on higher ground or sleeping in churches, schools and community facilities built to withstand hurricanes.

None of the shelters has yet been tested by Category 5 winds, however.